Pathogenic variants in cause a genetic disorder characterised by developmental delay/intellectual disability and a spectrum of neurobehavioural phenotypes including autism and ADHD.

Background: Rare variants in hundreds of genes have been implicated in developmental delay (DD), intellectual disability (ID) and neurobehavioural phenotypes. encodes a protein important for RNA silencing. Heterozygous truncating variants have been reported in three patients from large cohorts with autism, but no full phenotypic characterisation was described.

Methods: Clinical and molecular characterisation was performed on 17 patients with variants. Clinical data were obtained by retrospective chart review, parent interviews, direct patient interaction with providers and formal neuropsychological evaluation.

Results: Clinical findings included DD/ID (17/17) (speech delay in 94% (16/17), fine motor delay in 82% (14/17) and gross motor delay in 71% (12/17) of subjects), autism or autistic traits (13/17), attention deficit and hyperactivity disorder (ADHD) (11/17), other behavioural problems (7/17) and musculoskeletal findings (12/17). Other congenital malformations or clinical findings were occasionally documented. The majority of patients exhibited some dysmorphic features but no recognisable gestalt was identified. 17 heterozygous variants were identified in 12 male and five female unrelated subjects by exome sequencing (14), a targeted panel (2) and a chromosomal microarray (1). The variants were nonsense (7), frameshift (5), splice site (2), intragenic deletions (2) and missense (1).

Conclusions: Variants in cause a novel genetic disorder characterised by recurrent neurocognitive and behavioural phenotypes featuring DD/ID, autism, ADHD and other behavioural abnormalities. Our data highly suggest that haploinsufficiency is the most likely pathogenic mechanism. should be added to the growing list of genes of the RNA-induced silencing complex associated with ID/DD, autism and ADHD.